The present invention relates to electrical circuit transfer apparatus and, more particularly, to apparatus used to transfer between time-responsive and temperature-responsive circuitry used to control the operation of a microwave oven.
The use of temperature-monitoring apparatus in microwave ovens is well known. U.S. Pat. No. 3,975,720 illustrates one conventional arrangement of such apparatus, including a temperature-sensitive probe having a thermistor mounted in its tip and circuitry responsive to thermally-induced changes in the resistance of the thermistor to control the cooking operation of the oven or to activate an enunciator. The probe is connected to the oven's operating circuitry by a shielded cable and a plug which mates with a connector in the oven wall. A disadvantage associated with this particular arrangement is that separate means are required to transfer between the temperature-responsive circuitry and the time-responsive circuitry when the probe is used in an oven also having a conventional timing control. It is possible, therefore, to inadvertantly use the wrong control mode when cooking with the oven by failing to properly set the transfer means to interconnect either the time-responsive or temperature-responsive circuitry to the microwave energy generator of the oven.
In order to overcome this deficiency some prior art microwave ovens utilize circuit transfer apparatus which function in response to insertion or withdrawal of the probe cable plug into or from the connector mounted on the oven wall. Such prior art transfer apparatus typically include a retention jack which holds the plug and one or more separate micro switches which effect the circuit transfer. It is believed that all prior art transfer apparatus of this type employ commercially available micro switches rated to accept the full 15 amp current required to drive the microwave energy generator of the oven. In addition, these apparatus require relatively complex mounting structures to properly align the jack and separate micro switches, thereby increasing both the cost and the size of the device.
An alternative prior art transfer apparatus of this same general type uses plug acuated electronic circuitry to effect the circuit transfer. Of course, such apparatus is relatively expensive and, again, employs plug retaining structure separate from the circuit transfer means.